This invention relates to a toner for developing a static charged image to be used for a copying machine or a printer, a production method of the toner, an image forming method and an image forming apparatus using the toner.
Japanese Patent Publication Open to Public Inspection No. 2000-214629 discloses that a polymerized toner prepared by a suspension polymerization method or an emulsion polymerization method has particles each having a small diameter with a narrow diameter frequency and a shape of rounded corner since the diameter and the shape of the toner particles can be controlled in an aqueous medium in which the polymerization is performed. Such the toner is noted as a toner capable of reproducing a small dot of a digital image in accordance with high fine line reproducibility and high image resolving ability hereof.
The polymerized toner is required to have ability for suiting the recycling use since a technology of recycling use of the toner is applied also on such the toner. A problem is on such the toner, however, that the toner is deteriorated and finely powdered when the toner is subjected to mechanical shearing stress in the course of stirring in a developing device or conveying in a recycle means. Particularly in an image forming apparatus having the tone recycling means, the toner is placed in an environment in which the deterioration and formation of the fine powder of the toner tends to be accelerated since the tone is frequently subjected to the shearing stress in a long period.
The deterioration and the finely powdering of the toner is further made worse by formation of cracks on the surface of the toner particle caused by the action of ozone which decomposes organic substances since ozone formed at the time of light exposing for image formation exists in the image forming apparatus. Consequently, a countermeasure such that to inhibit the formation of ozone caused by the light exposure or that to provide a function of effectively exhaust ozone to the image forming apparatus is taken. However, the problems of the deterioration and the powdering of the toner are not sufficiently solved yet.
The fine powdered particle of the toner formed by the mechanical shearing stress in the developing device or the toner recycling means is easily scattered. Accordingly, the fine powder of the toner causes the contamination the triboelectric charging device or the photoreceptor and a problem of insufficient cleaning since the finely powdered toner particle is easily passed through the cleaning device. Moreover, the finely powdered toner is adhered on an image receiving medium such as a recording paper, and causes fogging at the non-imaged white background of the image. The finely powdered toner adhered and remained on the transfer electrode causes insufficient transfer, and a result of that, problems such as occurrence of contamination on the halftone image caused by the insufficient transfer, formation of contamination of the white background of the image receiving paper by the finely powdered toner passed trough the cleaning device, and formation of line shaped contamination on the halftone image by adhering of the finely powdered toner remained on the developing roller accompanied with the repeating of the image formation. Furthermore, an insufficient fixation is induced since the fixing ability of the fixing device is lowered by the accumulation of the scattered finely powdered toner in the fixing device. Such the problem is made serious when the image forming apparatus is used under a condition with a low temperature and a low humidity.
The invention is attained on the above-described background.
The first object of the invention is to provide a toner for developing a static charged image having sufficient ozone resistively, which is not deteriorated and not powdered in an atmosphere forming ozone.
The second object of the invention is to provide a toner for developing a static charged image usable in an image forming apparatus having atoner recycle means.
The third object of the invention is to provide a toner for developing a static charged image by which a clean electrophotographic image without formation of fogging on the white background and that of line-shape contamination or unevenness of the density in the halftone image.
The fourth object of the invention is to provide a toner for developing a static charged image excellent in the fixing ability, by which no insufficient fixation is occurred even when the image formation is carried out under a low temperature and low humidity condition.
The fifth object of the invention is to provide a toner for developing a static charged image by which a character image without spreading and a high quality image excellent in the fine line reproducibility can be stably obtained in a prolonged period.
And another object of the invention is to provide a toner for developing a static charged image wherein the toner particle itself has a high resistivity against ozone.
In the invention, it has been found that a toner particle in which the resin constituting the toner particle has a cell structure has a high durability and such the toner particle is not deteriorated and not powdered even when the toner particle is stirred in a prolonged period for image formation under a condition with the presence of a high concentration of ozone such as that in the developing device of the image forming apparatus.
The summary and preferable embodiments of the invention are described below.
A toner for developing a static charged image containing a toner particle at least comprising a resin and a colorant, wherein the resin constituting the toner particle has a cell structure having cells and a cell wall, and an average value of the FERE-horizontal diameters of the cells is from 20 to 200 nm and a variation coefficient of the FERE-horizontal diameters of the cells is from 10 to 35%.
The average value of the FERE-horizontal diameters is from 120 to 160 nm and the variation coefficient is preferably not more than 30%.
The toner particle preferably further contains a crystalline substance.
It is preferable that the colorant particles are distributed between the cells.
It is preferable in the toner particle containing the resin, the colorant and the crystalline substance that the colorant particles are distributed between the cells.
It is preferable in the toner particle containing the resin, the colorant and the crystalline substance that the crystalline substance is distributed between the cells.
It is preferable the number variation coefficient in the number size distribution is not more than 27 percent and the variation coefficient of said shape coefficient is not more than 16 percent.
It is preferable the ratio of toner particles without corners is at least 50 percent by number and the number variation coefficient in the number particle size distribution is 27 percent or less.
It is preferable that a number ratio of toner particles having a shape coefficient of 1.2 to 1.6 and is at least 65 percent, and further the variation coefficient of said shape coefficient is not more than 16 percent, and the number variation coefficient in the number particle size distribution is 27 percent or less.
The toner of the present invention preferably has a sum M of at least 70 percent. Said sum M is obtained by adding relative frequency m1 of toner particles, included in the most frequent class, to relative frequency m2 of toner particles included in the second frequent class in a histogram showing the particle diameter distribution, which is drawn in such a manner that natural logarithm lnD is used as an abscissa, wherein D (in xcexcm) represents the particle diameter of a toner particle, while being divided into a plurality of classes at intervals of 0.23, and the number of particles is used as an ordinate.
It is preferable that the toner has a number average particle diameter of 2 to 7 xcexcm.
The above-described toner particle is preferably produced by a production method having a process for polymerizing of a polymerizable monomer in an aqueous medium to form the resin particles.
The toner particle is preferably produced by a production method having a process for coagulating and adhering by fusion the resin particles.
The toner particle is preferably produced by a production method having a process in which the resin particles and the colorant particles are salted-out and adhered by fusion.
The toner particle is preferably produced by a production method having a process for producing the resin particle by multi-step polymerization and a process for salting-out and adhering by fusion the resin particles and the colorant particles.
The toner particle is preferably produced by the above-described production methods.
The toner particle is preferably produced by a production method having a process for adhering by fusion the resin particle onto the surface of the colorant particle by salting-out and adhering by fusion.
The toner is preferably applied for an image forming method by which a static latent image formed on a photoreceptor by digital exposure is visualized.
The toner is preferably applied for an image forming method in which the toner is repeatedly used by recycling.
The toner is preferably applied for an image forming apparatus which has a developing means for visualizing the static latent image formed on the photoreceptor by the use of the toner for developing the static charged image, a transfer means for transferring the visualized image onto a image receiving medium, and a fixing means for fixing by heat the visualized image transferred on the image receiving medium, and the light exposure to the photoreceptor is carried out by digital exposure and the ozone concentration in the atmosphere of the developing means is from 0.1 to 10 ppm.
The toner is preferably applied for an image forming apparatus which has a developing means for visualizing the static latent image formed on the photoreceptor by the use of the toner for developing the static charged image, a transfer means for transferring the visualized image onto a image receiving medium, a fixing means for fixing by heat the visualized image transferred on the image receiving medium and a means for recycling the toner.